看懂文章《美國初選和黨團會議》（https://www.bbc.com/news/world-us-canada-51273719）之前，筒子們需要解決2個單詞：primaries和caucus。文章先給出caucus的定義：
Caucus：
A caucus involves people attending a meeting - maybe for a few hours - before they vote on their preferred candidate, perhaps via a head count or a show of hands. Those meetings might be in just a few select locations - you can't just turn up at a polling station.
在詞典裡caucus的意思是：
“A meeting of the local members of a political party especially to select delegates to a convention
or register preferences for candidates running for office.”（黨團會議），在這段話我們可以看出黨團會議的幾個特徵：1. 數人頭數或舉手投票，因此不匿名；2. 有規定的投票站；3. 有規定的投票時間。
Primary:
Unlike a caucus, where voters are expected to turn up at a few limited locations at certain times and stick around for a while, primary voters can just turn up at a polling booth and vote in secret. Then leave.
在詞典裡primary的意思是“the process by which voters can indicate their preference for their party's candidate, or a candidate in general, in an upcoming general election, local election, or by-election, with the goal of narrowing the field of candidates.”（黨內初選）。黨內初選不同於黨團會議，投票人投票更為自由，黨內初選的特徵有：1. 匿名投票；2. 投票站更多；3. 投票時間更自由。
因此，兩者的區別可以這樣來說：caucus更側重於黨員投票決定，是由各政黨自己舉行的內部會議；而primary可以是開放式初選（非黨員和註冊黨員均可投票）和封閉式初選（註冊黨員投票），強調的是“匿名投票”。
但是2者最大的共性就是都是為了選取候選人參加競選，每個州的初選或黨團會議通常為間接選舉，選民並非直接決定總統候選人，而是選出候選人參加各黨提名大會。這些代表則會在大會上選出各黨總統候選人。
那麼美國大選的運作形式是怎樣的呢？通過文章我們可以看到：
每個州或地區先通過一系列的初選和黨團會議選擇候選人，2月3日先從愛荷華州開始，6月初在波多黎各自由邦結束。
今年共和黨候選人是特朗普，雖然從理論上來說他在黨內會有一個對手，但是由於特朗普在黨內的高支持率，今年共和黨內的競爭可能並無看頭。瞭解了這一點，民主黨內的初選就顯得大有看頭了。
過去一年，民主黨內有28名候選人宣佈競選總統候選人。但是由於資金不斷縮水、公眾反響不溫不火甚至有些冷淡以及互相攻擊，最後參加競選的只有11人。目前，這一數字已減至7人。
2月3日最先從愛荷華州開始的是一系列的黨團會議，而非初選。伯尼·桑德斯和皮特·布蒂吉格在愛荷華州的黨團會議上都有不俗的表現。今年，民主黨僅在美國的4個州（內華達州、北達科他州、懷俄明州和愛荷華州）有黨團會議。在任一一場黨團會議或初選中，候選人得票率不得低於15%。當所有候選人得票率都低於15%時，黨員可進行第二次投票。
愛荷華州重要嗎？
為何初選先從愛荷華州開始？這就不得不提到美國第39任總統吉米·卡特。1976年卡特競選總統之時，其競選團隊意識到先從愛荷華州競選可以抓住先發優勢。果不其然，卡特在愛荷華州的大獲全勝讓其勢不可擋，最終成為一匹黑馬當選美國總統。至此，愛荷華州成為候選人初選首發的必爭之地。
愛荷華州不重要嗎？
愛荷華州雖然從以上角度說很重要，但是它又沒那麼重要。自2000年以來，許多在愛荷華州獲勝的候選人都沒能最終成為總統候選人。
上述講到了從愛荷華州開始的是一系列的黨團會議，而非初選。那麼第一次初選是從哪個州開始的呢？新罕布什爾州。2月11日，位於美國東北部、僅有130萬人口的新罕布什爾州再次成為政治鬥爭的溫床。經過新罕布什爾州一役後，喬·拜登和伊麗莎白·沃倫大有可能成為民主黨候選人，儘管貝尼·桑德斯和皮特·布蒂吉格在新罕布什爾州獲得的黨代表票數最多。
好戲將於“超級星期二”3月3號開始
3月3日是初選日曆上的大日子。屆時將有16個州和地區、達2/3的黨代表為候選人投票。這天結束後，民主黨候選人將愈加明朗。
加利福利亞州和德克薩斯州是16個州和地區中擁有最多黨代表的兩個州。其中，加利福利亞州有415名黨代表，德克薩斯州有228名黨代表。這兩個州的人口非常多樣化，因此這兩個州的投票結果和愛荷華州、新罕布什爾州相比會有較大差別。
3月3號“超級星期二”過後，3月10號的星期二會成為又一個重要的日子。這一天將有6各州、352名黨代表投票。
特朗普大有可能於8月24至27號在北卡羅來納州夏洛特市召開的黨大會上宣誓成為共和黨候選人，民主黨則會於7月13至16號在威斯康星州密爾沃基市召開的黨大會上確認黨內候選人。
關於黨大會
假設在初選季，A候選人獲得了10個黨代表的支持。那麼，在黨大會期間這10個黨代表就會支持A候選人成為民主黨候選人。（任何一個黨員都可申請成為黨代表，黨代表一般是黨內積極分子或當地政治領導人。）
民主黨初選過程共有3979名黨代表。候選人在初選季若獲得超過50%也就是1990名黨代表的得票數，將在黨大會上成為黨內候選人。但是，如果候選人在初選季沒有獲得超過50%的黨代表支持率，就會出現“爭議大會”或“協商大會”的情況。解決的方法就是再次投票。
不同的是，再次投票過程中會加入771名“超級代表”。往屆或現任黨內高級官員都有可能成為“超級代表”，如前總統比爾·克林頓，現參議員佛蒙特和總統競選人貝尼·桑德斯。“超級代表”可自由投票。在再次投票過程中，候選人必須獲得50%也就是2376名黨代表的得票數才能成為黨內候選人。
上一屆總統大選，“超級代表”在黨大會第一次投票時和普通代表一起投票。但是很多代表在大會開始之前就已經是希拉里·克林頓的死忠粉了，認為該制度極不公平的貝尼·桑德斯於是開始推動變革。這一次，貝尼·桑德斯或許能夠從中受益了。
總統大選
黨大會之後，總統候選人離成為總統僅一步之遙——於11月3號舉行的總統大選。
英文原文
US election 2020: What are primaries and caucuses and how do they work?
Four years after the world watched Donald Trump's momentum build and build until he became the Republican nominee, America is again deciding who will run for the White House.
The nominees are being chosen through a series of primaries and caucuses in every US state and territory, that began in Iowa on 3 February and ends in Puerto Rico in early June.
The Republican nominee will be Donald Trump. Even though technically he has a challenger, he is so popular among Republicans, he has a clear run ahead of him. With that in mind, the Democratic primaries are the only ones worth watching.
It's an unusual process, not all of which makes sense, although we've tried.
Step one: The start line
A whole year before the primaries, the first candidates emerged from hibernation. Over the year, others woke up and eventually 28 people announced they were running to become the Democratic nominee for president.
But dwindling funds, luke-warm or (ice-cold) public reaction and campaign infighting have, to varying degrees, led to most of them pulling out of the race.
At the start of primary season, 11 people remained in the running, a number that has now reduced to seven. In theory, any one of them could become the nominee. In reality, only a few have a chance.
Step two: The Iowa caucuses
The first event of the primary season isn't a primary at all - it's a series of caucuses, in Iowa. These took place on Monday 3 February, in somewhat chaotic fashion.
What are caucuses?
A caucus involves people attending a meeting - maybe for a few hours - before they vote on their preferred candidate, perhaps via a head count or a show of hands. Those meetings might be in just a few select locations - you can't just turn up at a polling station.
As a result, caucuses tend to really suit candidates who are good at rousing their supporters to get out of bed. People like Bernie Sanders, for example, who performed well in Iowa this time, as did Pete Buttigieg.
Caucuses used to be far more popular back in the day, but this year, Democrats are holding only four in US states - in Nevada, North Dakota, Wyoming and Iowa.
If any candidate gets under 15% of the vote in any caucus, their supporters then get to pick a second choice from among the candidates who did get more than 15%, or they can just choose to sit out the second vote.
Why does Iowa matter?
A win there for any candidate can help give them momentum and propel them to victory in the primaries.
Why is Iowa first in the primary calendar? You can blame Jimmy Carter, sort of. Iowa became first in 1972, for various technical electoral reasons too boring to go into here. But when Carter ran for president in 1976, his team realised they could grab the momentum by campaigning early in Iowa. He won there, then surprisingly won the presidency, and Iowa's fate was sealed.
Why does Iowa not matter?
Iowa doesn't represent the entire US - it's largely white, so the way people vote there is very, very different than in other states.
Its record on picking the eventual nominees is a bit rubbish too, at least when it comes to Republicans - when there's an open Republican race, Iowa hasn't opted for the eventual nominee since 2000. Such names as Mike Huckabee, Rick Santorum and Ted Cruz have won there in recent years.
This year, Iowa suffered a bloody nose when the Democratic result was delayed by days due to technical glitches. Its curtain-raiser status may now be in doubt.
Step three: The New Hampshire primary
Eight days after Iowa on Tuesday, 11 February, was the first primary, in New Hampshire. The tiny north-eastern state of only 1.3m people once again became an unlikely hotbed of political activity.
What is a primary?
Unlike a caucus, where voters are expected to turn up at a few limited locations at certain times and stick around for a while, primary voters can just turn up at a polling booth and vote in secret. Then leave.
How does a primary work?
The more votes a candidate gets in a caucus or primary, the more "delegates" they are awarded, and all candidates will be hoping to win an unbeatable majority of delegates.
The number of delegates differs in each state, and is decided by a convoluted series of criteria. In California's primary, for example, there are 415 Democratic delegates up for grabs this year. In New Hampshire, it was only 24.
This year is a bit different. Any candidate would need to get at least 15% of the vote in any primary or caucus to be awarded delegates. There are still eight candidates in the running - an unusually large number - so there's a risk the vote share will be spread out and some of the candidates may struggle to reach 15%.
After New Hampshire, we started to get a clear picture of who was struggling (Joe Biden, Elizabeth Warren), but even though Bernie Sanders and Pete Buttigieg had claimed the most delegates at this stage, neither is guaranteed to become the nominee.
The picture should become much clearer on...
Step four: Super Tuesday
A few other states vote in between New Hampshire and the end of February, but this is when things really start to warm up: Super Tuesday, on 3 March.
What is Super Tuesday?
It is the big date in the primary calendar, when 16 states, territories or groups vote for their preferred candidate in primaries or caucuses. A third of all the delegates available in the entire primary season are up for grabs on Super Tuesday. By the end of the day it could be much clearer who the Democratic candidate will be.
The two states with the most delegates are voting on Super Tuesday - California (with 415 Democratic delegates) and Texas (228). California is voting three months earlier than in 2016, making Super Tuesday even more super than normal.
California and Texas are two states with very diverse populations, so we may see them going for very different candidates than those chosen in Iowa and New Hampshire.
Step five: The rest of the race
After hectic Super Tuesday, everyone gets to cool down for a week, before another busy day on Tuesday, 10 March, when six states vote, with 352 delegates available.
After that, the primary season still has three months left to run and at the end, the role of those delegates will become clear...
Donald Trump will almost certainly be sworn in as the Republican nominee at the party convention in Charlotte, North Carolina, between 24 and 27 August. The Democrats will confirm their candidate at their own convention between 13 and 16 July in Milwaukee, Wisconsin.
What happens in a convention?
Here's where those delegates come in.
Let's say that during primary season, candidate A wins 10 delegates. During the convention, those 10 delegates would vote for candidate A to become the Democratic nominee. (Any party member can apply to be a delegate - they tend to be party activists or local political leaders.)
All through the Democratic primaries, there are 3,979 delegates available. If any one candidate wins more than 50% of those delegates during primary season (that's 1,990 delegates), then they become the nominee in a vote at the convention.
But if we get to the Democratic convention and no-one has more than 50% of the delegates, it becomes what's known as a "contested" or "brokered" convention. This could well happen this year. There are so many candidates that no one frontrunner emerges in the primaries, and they split the delegates between them. In that circumstance, a second vote would follow.
In that second vote, all the 3,979 delegates would vote again, except this time they would be joined by an estimated 771 "superdelegates". These are senior party officials past and present (former president Bill Clinton is one, as is current Vermont senator and presidential contender Bernie Sanders), and they're free to vote for whomever they wish.
If a candidate wins 50% or more in that vote - 2,376 delegates - then they become the nominee.
This is all thanks to a rule change in 2020: last time around, the superdelegates voted at the start of the convention, with the delegates. But many had pledged their support to Hillary Clinton even before the convention, leading her rival Mr Sanders to suggest the deck was stacked against him.
He's the one who campaigned for the change - and it may benefit him in 2020.
Step seven: The presidency?
After inching past Iowa, negotiated New Hampshire, survived Super Tuesday and come through the convention, there is only one step left for the nominee: the presidential election, on 3 November.
We'll explain how that one works a little closer to the time.
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